1. Field of the Invention
The present invention relates to a multiple throttle device that is mounted on an engine having a plurality of cylinders.
2. Description of the Related Art
Motorcycles (vehicles) are equipped with an engine in which a plurality of cylinders are arranged in line for high power. In many engines for motorcycles, cylinders are arranged in a vehicle width direction to be compactly housed in space (engine room) under a fuel tank.
Such an engine for a motorcycle has a structure in which a multiple throttle device is mounted on each cylinder of the engine, or more specifically, on an intake port of each cylinder in order to secure responsiveness.
The multiple throttle device is a device in which one throttle valve is allocated to each of the intake ports, and the throttle valves are opened and closed in synchronization. This multiple throttle device has a structure in which intake passages leading to the intake ports of the engine are formed in a throttle body fixed to the engine; the throttle valves are allocated to the respective intake passages; and the throttle valves are supported by a long throttle shaft disposed in a juxtaposed direction of the valves. The throttle valves are simultaneously opened/closed by displacement of the throttle shaft.
More and more motorcycles are equipped with a throttle-by-wire multiple throttle device as with four-wheel vehicles. In the throttle-by-wire multiple throttle device, the throttle shaft is driven by a drive section including a motor and a gear mechanism for transmitting the power of the motor, and the opening of the throttle valves is detected by a sensor section made up of a throttle position sensor. This way, the multiple throttle device is capable of controlling the opening degree of the throttle valves according to a target opening degree.
The throttle position sensor is an important component in terms of controlling the throttle valves.
As disclosed in Unexamined Japanese Patent Publication No. 2004-132289, in a number of multiple throttle devices, the throttle position sensor is disposed in an end face of the throttle shaft that is inserted through the throttle body along the entire width (in the direction where the intake passages are arranged and along the entire length).
The throttle position sensor of this type is fixed to the end of the throttle shaft and thus placed in the outermost position of the throttle body. This allows the throttle position sensor to outwardly protrude from the end portion of the throttle body in the width direction as shown in Patent Document 1.
However, many of the motorcycles equipped with an engine in which cylinders are arranged in line include a cylinder line extending in the vehicle width direction in consideration of equipment capacity. The throttle position sensor is placed in the outermost position in the vehicle width direction according to the equipment of the engine.
The throttle position sensor practically increases the entire width of the throttle body, so that the throttle body is prone to contact the frame members disposed on both sides of the engine.
Also, if the motorcycle (vehicle) falls down, the throttle position sensor is likely to be damaged by hitting against the ground or the like.
One way of solving this problem is to set the throttle position sensor in the drive section for driving the throttle shaft, for example, a gear for transmitting a drive force from the motor to the throttle shaft. On the other hand, if the foregoing structure is employed, a conventional method for detecting the shaft displacement has to be utterly changed to a method for detecting the displacement of a special gear, so that the sensor section needs to have a special structure, resulting in a considerable cost increase. On this account, it is difficult to employ the above-mentioned structure.